Flow Rate Monitor for Fluid Cooled Microwave Ablation Probe

ABSTRACT

A microwave ablation system includes a generator operable to output energy and an ablation probe coupled to the generator that delivers the energy to a tissue region. The ablation system also includes a controller operable to control the generator and at least one sensor coupled to the ablation probe and the controller that detects an operating parameter of the ablation probe. The controller performs a system check by ramping up an energy output of the generator from a low energy level to a high energy level and monitors an output from the sensor at predetermined intervals of time during the system check to determine an abnormal state. The controller controls the generator to cease the energy output when the controller determines an abnormal state.

BACKGROUND

1. Technical Field

The present disclosure relates generally to microwave ablationprocedures that utilize microwave surgical devices having a microwaveantenna which may be inserted directly into tissue for diagnosis andtreatment of diseases. More particularly, the present disclosure isdirected to a system and method for verifying correct system operationof a microwave ablation system.

2. Background of Related Art

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures (which areslightly lower than temperatures normally injurious to healthy cells.)These types of treatments, known generally as hyperthermia therapy,typically utilize electromagnetic radiation to heat diseased cells totemperatures above 41° C., while maintaining adjacent healthy cells atlower temperatures where irreversible cell destruction will not occur.Other procedures utilizing electromagnetic radiation to heat tissue alsoinclude ablation and coagulation of the tissue. Such microwave ablationprocedures, e.g., such as those performed for menorrhagia, are typicallydone to ablate and coagulate the targeted tissue to denature or kill thetissue. Many procedures and types of devices utilizing electromagneticradiation therapy are known in the art. Such microwave therapy istypically used in the treatment of tissue and organs such as theprostate, heart, liver, lung, kidney, and breast.

One non-invasive procedure generally involves the treatment of tissue(e.g., a tumor) underlying the skin via the use of microwave energy. Themicrowave energy is able to non-invasively penetrate the skin to reachthe underlying tissue. However, this non-invasive procedure may resultin the unwanted heating of healthy tissue. Thus, the non-invasive use ofmicrowave energy requires a great deal of control.

Presently, there are several types of microwave probes in use, e.g.,monopole, dipole, and helical. One type is a monopole antenna probe,which consists of a single, elongated microwave conductor exposed at theend of the probe. The probe is typically surrounded by a dielectricsleeve. The second type of microwave probe commonly used is a dipoleantenna, which consists of a coaxial construction having an innerconductor and an outer conductor with a dielectric junction separating aportion of the inner conductor. The inner conductor may be coupled to aportion corresponding to a first dipole radiating portion, and a portionof the outer conductor may be coupled to a second dipole radiatingportion. The dipole radiating portions may be configured such that oneradiating portion is located proximally of the dielectric junction, andthe other portion is located distally of the dielectric junction. In themonopole and dipole antenna probes, microwave energy generally radiatesperpendicularly from the axis of the conductor.

The typical microwave antenna has a long, thin inner conductor thatextends along the axis of the probe and is surrounded by a dielectricmaterial and is further surrounded by an outer conductor around thedielectric material such that the outer conductor also extends along theaxis of the probe. In another variation of the probe that provides foreffective outward radiation of energy or heating, a portion or portionsof the outer conductor can be selectively removed. This type ofconstruction is typically referred to as a “leaky waveguide” or “leakycoaxial” antenna. Another variation on the microwave probe involveshaving the tip formed in a uniform spiral pattern, such as a helix, toprovide the necessary configuration for effective radiation. Thisvariation can be used to direct energy in a particular direction, e.g.,perpendicular to the axis, in a forward direction (i.e., towards thedistal end of the antenna), or combinations thereof.

Invasive procedures and devices have been developed in which a microwaveantenna probe may be either inserted directly into a point of treatmentvia a normal body orifice or percutaneously inserted. Such invasiveprocedures and devices potentially provide better temperature control ofthe tissue being treated. Because of the small difference between thetemperature required for denaturing malignant cells and the temperatureinjurious to healthy cells, a known heating pattern and predictabletemperature control is important so that heating is confined to thetissue to be treated. For instance, hyperthermia treatment at thethreshold temperature of about 41.5° C. generally has little effect onmost malignant growth of cells. However, at slightly elevatedtemperatures above the approximate range of 43° C. to 45° C., thermaldamage to most types of normal cells is routinely observed. Accordingly,great care must be taken not to exceed these temperatures in healthytissue.

In the case of tissue ablation, a high radio frequency electricalcurrent in the range of about 500 MHz to about 10 GHz is applied to atargeted tissue site to create an ablation volume, which may have aparticular size and shape. Ablation volume is correlated to antennadesign, antenna performance, antenna impedance and tissue impedance. Theparticular type of tissue ablation procedure may dictate a particularablation volume in order to achieve a desired surgical outcome. By wayof example, and without limitation, a spinal ablation procedure may callfor a longer, narrower ablation volume, whereas in a prostate ablationprocedure, a more spherical ablation volume may be required.

Microwave ablation devices utilize sensors to determine if the system isworking properly. However, without delivery of microwave energy, thesensors may indicate that the probe assembly status is normal. Further,defects in antenna assemblies may not be apparent except at high powers.As such, when microwave ablation system is tested using a low powerroutine, a post manufacture defect may not be apparent. This isespecially important for high power microwave ablation devices, wherefailures may result in extremely high temperatures and flying debris.

Fluid cooled or dielectrically buffered microwave ablation devices mayalso be used in ablation procedures to cool the microwave ablationprobe. Cooling the ablation probe may enhance the overall ablationpattern of antenna, prevent damage to the antenna and prevent harm tothe clinician or patient. However, during operation of the microwaveablation device, if the flow of coolant or buffering fluid isinterrupted, the microwave ablation device may exhibit rapid failuresdue to the heat generated from the increased reflected power.

SUMMARY

The present disclosure provides a microwave ablation system. Themicrowave ablation system includes a generator operable to outputenergy, an ablation probe coupled to the generator that is operable todeliver the energy to a tissue region, a controller operable to controlthe generator, and at least one or more sensors coupled to the ablationprobe and the controller. The sensor detects an operating parameter ofthe ablation probe. The controller performs a system check by ramping upan energy output of the generator from a low energy level to a highenergy level and monitors an output from the at least one sensor atpredetermined intervals of time during the system check to determine anabnormal state. The controller controls the generator to cease theenergy output when the controller determines an abnormal state.

In embodiments, the sensor detects a temperature of the ablation probe,radiating behavior of the ablation probe, fluid pressure, forward andreflective power and fluid flow of coolant.

In yet another embodiment of the microwave ablation system, the sensoris a thermocouple, thermistor, optical fiber, receiving antenna,rectenna, radio frequency power sensor, pressure sensor resistivejunction or capacitive junction.

The present disclosure also provides a method of detecting an abnormalstate in a microwave ablation system. The method includes the steps ofoutputting a low energy level from a generator to an ablation probe anddetecting an operational parameter of the ablation probe at the lowenergy level. The detected operational parameter is compared to apredetermined range for the operational parameter and an energy leveloutput of the generator is increased in response to the comparison. Themicrowave ablation system ceases output of energy from the generator inresponse to the detected operational parameter being outside thepredetermined range.

In embodiments, the operational parameter is a temperature of theablation probe, radiating behavior of the ablation probe, fluidpressure, forward and reflective power, coolant flow in the probe andinsertion depth of probe.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 shows a representative diagram of a variation of a microwaveantenna assembly in accordance with an embodiment of the presentdisclosure;

FIGS. 2A-2C show graphs of time versus power in accordance withembodiments of the present disclosure;

FIG. 3 shows a system block diagram according to an embodiment of thepresent disclosure;

FIG. 4 shows a system block diagram according to another embodiment ofthe present disclosure; and

FIG. 5 shows a flow chart describing a ramping procedure according to anembodiment of the present disclosure.

DETAILED DESCRIPTION

Particular embodiments of the present disclosure are describedhereinbelow with reference to the accompanying drawings; however, it isto be understood that the disclosed embodiments are merely exemplary ofthe disclosure and may be embodied in various forms. Well-knownfunctions or constructions are not described in detail to avoidobscuring the present disclosure in unnecessary detail. Therefore,specific structural and functional details disclosed herein are not tobe interpreted as limiting, but merely as a basis for the claims and asa representative basis for teaching one skilled in the art to variouslyemploy the present disclosure in virtually any appropriately detailedstructure.

Like reference numerals may refer to similar or identical elementsthroughout the description of the figures. As shown in the drawings anddescribed throughout the following description, as is traditional whenreferring to relative positioning on a surgical instrument, the term“proximal” refers to the end of the apparatus which is closer to theuser and the term “distal” refers to the end of the apparatus which isfurther away from the user. The term “clinician” refers to any medicalprofessional (i.e., doctor, surgeon, nurse, or the like) performing amedical procedure involving the use of embodiments described herein.

Electromagnetic energy is generally classified by increasing energy ordecreasing wavelength into radio waves, microwaves, infrared, visiblelight, ultraviolet, X-rays and gamma-rays. As used herein, the term“microwave” generally refers to electromagnetic waves in the frequencyrange of 300 megahertz (MHz) (3×10⁸ cycles/second) to 300 gigahertz(GHz) (3×10¹¹ cycles/second). As used herein, the term “RF” generallyrefers to electromagnetic waves having a lower frequency thanmicrowaves. The phrase “ablation procedure” generally refers to anyablation procedure, such as RF or microwave ablation or microwaveablation-assisted resection. The phrase “transmission line” generallyrefers to any transmission medium that can be used for the propagationof signals from one point to another.

FIG. 1 shows a microwave antenna assembly 100 in accordance with oneembodiment of the present disclosure. Antenna assembly 100 includes aradiating portion 12 that is connected by feedline 110 (or shaft) viacable 15 to connector 16, which may further connect the assembly 100 toa power generating source 28, e.g., a microwave or RF electrosurgicalgenerator. Assembly 100, as shown, is a dipole microwave antennaassembly, but other antenna assemblies, e.g., monopole or leaky waveantenna assemblies, may also utilize the principles set forth herein.Distal radiating portion 105 of radiating portion 12 includes a taperedend 120 that terminates at a tip 123 to allow for insertion into tissuewith minimal resistance. It is to be understood, however, that taperedend 120 may include other shapes, such as without limitation, a tip 123that is rounded, flat, square, hexagonal, cylindroconical or any otherpolygonal shape.

An insulating puck 130 is disposed between distal radiating portion 105and proximal radiating portion 140. Puck 130 may be formed from anysuitable elastomeric or ceramic dielectric material by any suitableprocess. In some embodiments, the puck 130 is formed by overmolding frompolyether block amide (e.g., Pebax® sold by Arkema), polyetherimide(e.g., Ultem® and/or Extem® sold by SABIC Innovative Plastics),polyimide-based polymer (e.g., Vespel® sold by DuPont), or ceramic. Asbest illustrated in FIG. 2, puck 130 includes coolant inflow port 131and coolant outflow port 133 to respectively facilitate the flow ofcoolant into, and out of, coolant chamber 148 of trocar 122 as furtherdescribed hereinbelow.

FIG. 2A is a graph depicting an operation of the microwave ablationsystem according to an embodiment of the invention. As depicted in FIG.2A, at t=0, the energy output from the generator is 0 W. As t increases,the energy output also increases at a constant slope Δ. Slope Δ issufficient to prevent any harm to a clinician or patient and to preventand damage to the system. When t=ramp, with ramp being a value of timesufficient to determine if the microwave ablation system ismalfunctioning, the energy output increases to an energy level, e.g.,140 W, sufficient to perform a microwave ablation procedure. During theramping procedure (0<t<ramp), the microwave ablation system performs asystem check to determine if the system is in proper working order or ifthe system is malfunctioning. If the system is malfunctioning, an energyoutput from the generator is ceased thereby preventing any harm to aclinician or patient or preventing any further damage to the microwaveablation system.

Alternatively, as shown in FIGS. 2B and 2C, a series of pulses may beused during the start up procedure. As shown in FIG. 2B, the series ofpulses have a constant amplitude with a pulse width t_(W). A duty cyclefor the pulses may be varied in order to adequately check the systemwithout harming the patient or the clinician. Alternatively, as shown inFIG. 2C, the series of pulses during the start up procedure may have apulse width T_(W) and vary in amplitude. The amplitude of the pulses maygradually reach an energy level sufficient to perform a microwaveablation procedure.

By utilizing a system check that gradually subjects the device toincreasing operational stresses (while monitoring sensor status) willallow for microwave ablation systems to limit the number of devices thatare damaged due to operator error, such as not turning on the coolingfluid pump. It will also reduce the likelyhood of patient and/or userinjury from potentially defective assemblies or from user error.

With reference to FIG. 3, a microwave ablation system, shown generallyas 600, according to an embodiment of the disclosure is depicted. System600 has an antenna assembly 610 that imparts microwave energy to apatient. Antenna assembly 610 is similar to antenna assembly 100described above or antenna assembly may be a choked wet tip (CWT)antenna because the antenna performance needs cooling for power andtissue matching. Generator 620, which is substantially similar to powergenerating source 28, is coupled to antenna assembly 610 and provides asource of energy thereto. Controller 630 is coupled to generator 620 andis configured to control generator 620 based on an input or signal fromsensor 640. Controller 630 may be a microprocessor or any logic circuitable to receive an input or signal from sensor 640 and provide an outputto control generator 620. Sensor 640 may be a thermocouple, thermistor,optical fiber, receiving antenna, rectenna, radio frequency powersensor, pressure sensor resistive junction or capacitive junction.Sensor 640 may be a single sensor or an array of sensors to detectoperational parameters of the antenna assembly 610 in order to determineif the microwave ablation system 600 is functioning properly. If thesensor 640 detects an abnormal value or level, the controller 630controls the generator 620 to cease an energy output. Sensor 640 may beincorporated into antenna assembly 610 or controller 630 or may becoupled to either antenna assembly 610 and/or controller 630. Microwaveablation system 600 may also be incorporated in antenna assembly 610 ormay be arranged in two or more devices. For instance, controller 630 andgenerator 620 may be incorporated in a single device or may be separatedevices.

Sensor 640 may be a temperature sensor to detect the temperature of theantenna assembly 610. Temperature sensor may be a thermocouple,thermistor or an optical fiber. A thermocouple is a junction between twodifferent metals that produces a voltage related to a temperaturedifference. Thermocouples are can also be used to convert heat intoelectric power. Any circuit made of dissimilar metals will produce atemperature-related difference of voltage. Thermocouples for practicalmeasurement of temperature are made of specific alloys, which incombination have a predictable and repeatable relationship betweentemperature and voltage. Different alloys are used for differenttemperature ranges and to resist corrosion. Where the measurement pointis far from the measuring instrument, the intermediate connection can bemade by extension wires, which are less costly than the materials usedto make the sensor. Thermocouples are standardized against a referencetemperature of 0 degrees Celsius. Electronic instruments can alsocompensate for the varying characteristics of the thermocouple toimprove the precision and accuracy of measurements.

A thermistor is a type of resistor whose resistance varies withtemperature. Thermistors are widely used as inrush current limiters,temperature sensors, self-resetting overcurrent protectors, andself-regulating heating elements. The material used in a thermistor isgenerally a ceramic or polymer. Thermistors typically achieve a highprecision temperature response within a limited temperature range.

Sensor 640 may also be used to monitor radiating behavior, e.g., areceiving antenna or a rectenna. The receiving antenna receivesradiation from the antenna assembly and provides an electrical signal toindicate the level of radiation. A rectenna is a rectifying antenna, aspecial type of antenna that is used to directly convert microwaveenergy into DC electricity. Its elements are usually arranged in amulti-element phased array with a mesh pattern reflector element to makeit directional. A simple rectenna can be constructed from a Schottkydiode placed between antenna dipoles. The diode rectifies the currentinduced in the antenna by the microwaves.

Sensor 640 may also be an RF power sensor that monitors forward andreflected power. The RE power sensor measures the power output of thegenerator 620 that is utilized by the antenna assembly 610. It can alsomeasure reflected power which is RF energy that is reflected from theablated tissue region and received by the antenna assembly.

Sensor 640 may also be a pressure sensor for monitoring fluid and/or gaspressure. Pressure sensor generates a signal related to the pressureimposed. Typically, such a signal is electrical, but optical, visual,and auditory signals are also contemplated. Pressure sensors can beclassified in terms of pressure ranges they measure, temperature rangesof operation, and most importantly the type of pressure they measure. Interms of pressure type, pressure sensors can be divided into fivecategories. Absolute pressure sensors which measure the pressurerelative to perfect vacuum pressure (0 PSI or no pressure). Gaugepressure sensors may be used in different applications because it can becalibrated to measure the pressure relative to a given atmosphericpressure at a given location. Vacuum pressure sensors are used tomeasure pressure less than the atmospheric pressure at a given location.Differential pressure sensors measure the difference between two or morepressures introduced as inputs to the sensing unit. Differentialpressure sensors may also be used to measure flow or level inpressurized vessels. Sealed pressure sensors are similar to the gaugepressure sensors except that it is previously calibrated bymanufacturers to measure pressure relative to sea level pressure.

With reference to FIG. 4, a microwave ablation system, shown generallyas 700, according to an embodiment of the present disclosure isdepicted. Microwave ablation system 700 may be similar to ablationsystems described above with regard to FIGS. 1 and 3. The system 700includes an ablation device 702 having an antenna 702 a and a handle 702b used to ablate tissue. Generator 706 supplies the ablation device withenergy via coaxial cable 704. Ablation device 702 is supplied withcoolant or buffering fluid from coolant supply 710 through conduit 708.The coolant flows through the ablation device 702 as described above andexits the ablation device 702 via conduit 708 into chamber 714. Conduit708 may be a multi lumen conduit having an inflow lumen for supplyingthe ablation device 702 with coolant and an outflow lumen for coolant toexit the ablation device 702 into the chamber 714. Additionally, conduit708 may be provided as two separate conduits, an inflow conduit and anoutflow conduit.

As shown in FIG. 4, a sensor 712 is provided to monitor the flow ratethrough conduit 708. As described above, when coolant circulation isinterrupted, the ablation device 702 may tend to exhibit rapid failures.By monitoring the fluid flow, damage to the ablation device 702 as wellas harm to the clinician or patient can be prevented. Sensor 712provides an electrical signal to the controller 716 that represents areal-time fluid flow measurement or pressure measurement. Controller 716compares the electrical signal to a predetermined range. If theelectrical signal is within a predetermined range, the controller 716signals the generator 706 to continue with the ablation procedure. Ifthe electrical signal is outside the predetermined range, the controller716 controls the generator 706 to cease the ablation procedure. Sensor712 may be placed anywhere along the fluid path. For instance, sensor712 may be placed in antenna 702 a, handle 702 b or along the inflowlumen/conduit or outflow lumen/conduit. The sampling rate of sensor 712should be sufficient enough to catch intermittent problems with the flowof fluid through the ablation system 700. Sensor 712 may be configuredto detect the fluid flow during startup before microwave energy isdelivered to the ablation device or during an ablation procedure.

Sensor 712 may be a pressure sensor similar to the pressure sensordescribed above with regard to FIG. 3. The pressure sensor measures thefluid pressure of the coolant or dielectric buffer and provides anelectrical signal to the controller 716.

In some embodiments, sensor 712 may also be a fluid flow meter. Thereare many different types of fluid flow meters that can be used tomeasure the flow rate. In a differential pressure flow meter, the flowis calculated by measuring the pressure drop over an obstructionsinserted in the flow. The differential pressure flowmeter is based onthe Bernoulli's Equation, where the pressure drop and the furthermeasured signal is a function of the square of the flow speed. In avelocity flowmeter the flow is calculated by measuring the speed in oneor more points in the flow, and integrating the flow speed over the flowarea. In a calorimetric flowmeter, two temperature sensors in closecontact with the fluid but thermally insulated from each other are used.One of the two sensors is constantly heated and the cooling effect ofthe flowing fluid is used to monitor the flowrate. In a stationary (noflow) fluid condition there is a constant temperature difference betweenthe two temperature sensors. When the fluid flow increases, heat energyis drawn from the heated sensor and the temperature difference betweenthe sensors is reduced. The reduction is proportional to the flow rateof the fluid. Response times will vary due the thermal conductivity ofthe fluid. In general lower thermal conductivity require higher velocityfor proper measurement. The calorimetric flowmeter can achieverelatively high accuracy at low flow rates.

An electromagnetic flowmeter operates on Faraday's law ofelectromagnetic induction that states that a voltage will be inducedwhen a conductor moves through a magnetic field. The liquid serves asthe conductor and the magnetic field is created by energized coilsoutside the flow tube. The voltage produced is directly proportional tothe flow rate. Two electrodes mounted in the pipe wall detect thevoltage that is measured by a secondary element. Electromagneticflowmeters can measure difficult and corrosive liquids and slurries, andthey can measure flow in both directions with equal accuracy.Electromagnetic flowmeters have a relatively high power consumption andcan only be used for electrical conductive fluids such as water.

Ultrasonic flow meters measure the difference of the transit time ofultrasonic pulses propagating in and against flow direction. This timedifference is a measure for the average velocity of the fluid along thepath of the ultrasonic beam. By using the absolute transit times boththe averaged fluid velocity and the speed of sound can be calculated. Ifa fluid is moving towards a transducer, the frequency of the returningsignal will increase. As fluid moves away from a transducer, thefrequency of the returning signal decrease. The frequency difference isequal to the reflected frequency minus the originating frequency and canbe use to calculate the fluid flow speed.

A positive displacement flowmeter measures process fluid flow byprecision-fitted rotors as flow measuring elements. Known and fixedvolumes are displaced between the rotors. The rotation of the rotors areproportional to the volume of the fluid being displaced. The number ofrotations of the rotor is counted by an integral electronic pulsetransmitter and converted to volume and flow rate. The positivedisplacement rotor construction can be done in several ways:reciprocating piston meters (of single and multiple-piston types); andoval-gear meters having two rotating, oval-shaped gears withsynchronized, close fitting teeth. With oval-gear meters, a fixedquantity of liquid passes through the meter for each revolution. Shaftrotation can be monitored to obtain specific flow rates.

With reference to FIG. 5, an operation of the ramping procedure isshown. The procedure starts at step 802 where the microwave ablationsystem is started. At step 804, t is set to t₀ where t is time and t_(o)is the initial startup time. At step 806, a low energy level isoutputted from the generator 28 to the antenna assembly 100. The sensordetects an operational parameter, such as temperature of the ablationprobe, radiating behavior of the ablation probe, fluid pressure, forwardand reflective power, fluid flow of coolant or insertion depth of probe,of the antenna assembly 100 as described above in step 808. In step 810,the detected operational parameter is compared to a predetermined rangeof values stored in the controller. The predetermined range of valuesmay be set by a clinician or they may be stored in the controller by amanufacturer of the microwave ablation system. If the detectedoperational parameter is within the predetermined range, the procedureproceeds to step 812 where a determination is made as to whether t isless than t_(RAMP). If t is less than t_(RAMP), then the procedureproceeds to step 814 where t is increased in predetermined intervals. tcan be increased in intervals of N seconds or N minutes where N is anypositive integer. In step 816 the energy level output of the generatoris increased and steps step 808, step 810 and step 812 are repeated.When t is no longer less than t_(RAMP), the procedures proceeds to step820 where the ablation procedure is started and used on a patient. Ifthe controller makes a determination in step 810 that the detectedoperational parameter in step 808 is not within the predetermined range,the procedure proceeds to step 818 where the controller controls thegenerator to cease energy output.

The ramping procedure outlined above may avoid an assembly failure andpotential clinician or patient injury. Although FIG. 5 depicts aparticular arrangement of steps to perform the system check during aramping procedure, it should be understood that a different arrangementof steps may be used while still falling under the scope of the presentdisclosure. During the ramping procedure and upon detection of abnormalsensor information, the power ramp would cease and return to zero. Theramp may be made long enough to reliably detect common malfunctionmechanisms. Redundant circuit designs or redundant multiple sensor typesmay provide a form of sensor control.

For instance, if the cooling fluid pump is turned off and no fluid is inthe antenna assembly, a pressure sensor may return abnormal pressurelevels. As such, a power ramp would cease and the power does not reach alevel where the coaxial cable would fail due to lack of cooling. If theantenna assembly is full of cooling fluid but the pump is not running,an abnormal reading from the pressure sensor or a rising temperaturefrom a thermo probe would indicate that cooling of the probe is notsufficient most likely due to lack of flow. Therefore, the power rampwould cease and the power does not reach a level where the coaxial cablewould fail due to lack of circulation.

In another example, if the device is not inserted into tissue resultingin a dangerous electromagnetic field pattern, a electromagnetic fielddetector such as the receiving antenna or rectenna would indicateabnormally high electromagnetic field levels along the shaft or aroundthe handle of the antenna. The detection of the high electromagneticfield levels would prevent an unintended clinician or patient burn.

When the antenna assembly is subjected to high powers, defects maybecome readily apparent. On ramp up, the sensors indicate abnormaloperating conditions thereby preventing the power level from reaching alevel sufficient to cause device failure and avoiding clinician orpatient injury.

Utilizing a test routine of the ablation probe which gradually subjectsthe device to increasing operational stresses while monitoring sensorstatus will allow for MWA systems to limit the number of devices whichare damaged due to operator error, such as not turning on the coolingfluid pump. It will also reduce the likely hood of patient and/or userinjury from potentially defective assemblies or from user error. This isespecially important for high power microwave ablation devices, wherefailures may result in extremely high temperatures and flying debris.

The described embodiments of the present disclosure are intended to beillustrative rather than restrictive, and are not intended to representevery embodiment of the present disclosure. Various modifications andvariations can be made without departing from the spirit or scope of thedisclosure as set forth in the following claims both literally and inequivalents recognized in law.

1. A microwave ablation system, comprising: a generator operable tooutput energy; an ablation probe coupled to the generator, the ablationprobe operable to deliver energy to tissue; a controller operable tocontrol the generator; and at least one sensor coupled to the ablationprobe and the controller, the at least one sensor operable to detect anoperating parameter of the ablation probe, wherein the controller isconfigured to perform a system check by ramping up an energy output ofthe generator from a low energy level to a high energy level and monitoran output from the at least one sensor at predetermined intervals oftime during the system check to determine an abnormal state, and whereinthe controller is configured to control the generator to cease theenergy output when the controller determines the abnormal state.
 2. Themicrowave ablation system according to claim 1, wherein the operationalparameter is a temperature of the ablation probe.
 3. The microwaveablation system according to claim 2, wherein the at least one sensor isa thermocouple, thermistor, or optical fiber.
 4. The microwave ablationsystem according to claim 1, wherein the operational parameter is aradiating behavior.
 5. The microwave ablation system according to claim4, wherein the at least one sensor is a receiving antenna or rectenna.6. The microwave ablation system according to claim 1, wherein theoperational parameter is forward and/or reflected power.
 7. Themicrowave ablation system according to claim 6, wherein the at least onesensor is a radio frequency power sensor.
 8. The microwave ablationsystem according to claim 1, wherein the operational parameter is fluidpressure.
 9. The microwave ablation system according to claim 8, whereinthe at least one sensor is a pressure sensor.
 10. The microwave ablationsystem according to claim 1, further comprising a coolant supplyconfigured to supply the ablation probe with coolant.
 11. The microwaveablation system according to claim 10, wherein the operational parameteris fluid flow of the coolant.
 12. A method of detecting an abnormalstate in a microwave ablation system, the method comprising the stepsof: outputting a low energy level from a generator to an ablation probe;detecting an operational parameter of the ablation probe at the lowenergy level; comparing the detected operational parameter to apredetermined range for the operational parameter; increasing an energylevel output of the generator in response to the comparison; and ceasingoutput of energy from the generator in response to the detectedoperational parameter being outside the predetermined range.
 13. Themethod according to claim 12, wherein the operational parameter is atemperature of the ablation probe.
 14. The method according to claim 12,wherein the operational parameter is a radiating behavior.
 15. Themethod according to claim 12, wherein the operational parameter isforward power or reflected power.
 16. The method according to claim 12,wherein the operational parameter is fluid pressure.
 17. The methodaccording to claim 12, wherein the operational parameter is flow ofcoolant in the ablation probe.